JP2006266140A - Piston of reciprocating fluid machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston for a reciprocating fluid machine, of which the weight can be reduced while at the same time securing required mechanical strength. <P>SOLUTION: This piston is a one-piece molded article made of an aluminum alloy or a magnesium alloy, including a piston head 46, a piston tail 32, and an intermediate section 48 connecting the piston head 46 and the piston tail 32. The intermediate section 48 has a pair of reinforcing ribs 50 and a semi-cylindrical outer peripheral wall 56 partly surrounding the reinforcing ribs 50. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston for a reciprocating fluid machine, and more particularly to a piston for a swash plate type or swash ring type refrigerant compressor incorporated in a refrigeration circuit for a vehicle as a reciprocating fluid machine.

  The piston of this type of refrigerant compressor is generally composed of a plurality of parts, which are welded together to form a single piston. Specifically, these parts include a piston body and a piston tail welded to the piston body at the rear end. In the case of a swash plate compressor, the piston tail can hold a pair of shoes therein, and these shoes are used for slidably sandwiching the swash plate.

The above-described split type piston is not only heavy but also expensive to manufacture, and is not suitable for a refrigerant compressor for vehicles.
On the other hand, the piston disclosed in Patent Document 1 is made of an aluminum alloy and is an integrally molded product formed by forging or casting. More specifically, the piston of Patent Document 1 has a hollow portion between the piston head and the piston tail in addition to the piston body and the piston tail. Since such a hollow portion reduces the weight of the entire piston, that is, its inertial mass, the piston of Patent Document 1 is considered suitable for high-speed reciprocating motion.
European Patent No. 814261 (EP 0814261 B1)

  However, in the case of the piston of Patent Document 1, since the hollow portion is opened on both sides of the piston as viewed in the circumferential direction of the swash plate, the presence of the hollow portion reduces the mechanical strength of the piston. For this reason, when the compression pressure of the refrigerant is applied to the piston head, the piston is easily subjected to compression deformation. Further, the tangential force generated by the friction between the swash plate and the pair of shoes of the piston causes the piston to bend and deform. Since the compression and bending deformation of the piston increases the sliding resistance of the piston with respect to the cylinder bore, the wear of the piston and the cylinder bore is undesirably promoted, and the load required for driving the compressor also increases. To do.

  An object of the present invention is to provide a piston of a reciprocating fluid machine that can be reduced in weight while ensuring mechanical strength.

A reciprocating fluid machine to which a piston that achieves the above object is applied includes a casing for housing a rotatable swash member, a cylinder block, and a cylinder bore into which the piston is reciprocally fitted. A cylinder block, and a radial surface including a rotation axis of the swash member and an axis of the cylinder bore.
The piston is an integrally molded product, and includes a piston head, a piston tail having a socket for a shoe that engages with the swash member, and an intermediate section that connects between the piston head and the piston tail. The intermediate section includes a plurality of reinforcing ribs arranged symmetrically around the radial surface in the vicinity of the radial surface and extending parallel to each other along the radial surface. ).

  When the swash member is rotated, the rotation of the swash member is converted into a linear motion of the piston through the shoe, and the piston reciprocates with the piston head slidingly contacting the inner peripheral surface of the cylinder bore. The fluid machine performs a series of processes from suction to discharge of the working fluid by the reciprocating motion of the piston. At this time, the pressure of the compressed working fluid is transmitted to the swash member through the piston head and the reinforcing rib. It is received by the swash member.

  The intermediate section of the piston may further include a substantially semi-cylindrical outer peripheral wall at least partially in sliding contact with the inner peripheral surface of the cylinder bore. The outer peripheral wall partially includes the reinforcing rib around the axis of the piston. (Claim 2). In this case, the outer peripheral wall has an opening area partly cut away, and the reinforcing rib is exposed through the opening area. Preferably, the outer peripheral wall has a symmetrical cross-sectional shape centered on the radial plane and has both side edges extending along the radial plane. During the reciprocating motion of the piston, side force is applied to the piston due to friction between the swash member and the shoe, and this side force is received by the inner peripheral surface of the cylinder bore through the outer peripheral wall described above.

More specifically, the outer peripheral wall has a circumferential length defined between its side edges, the circumferential length being reduced from the piston head toward the piston tail (claim 4). The outer shape of the outer peripheral wall is determined based on the computer-aided engineering (CAE) in consideration of the side force described above.
Furthermore, it is preferable that at least a part of the reinforcing rib of the piston has a slide guide that is in sliding contact with the inner peripheral surface of the cylinder bore. Such a slide guide increases the sliding surface of the piston with respect to the inner peripheral surface of the cylinder bore, and stabilizes the reciprocating motion of the piston.

  Furthermore, when the piston reciprocates, the piston tail slides into contact with the inner surface of the casing to prevent rotation around the axis of the piston, and opens to the stopper surface to connect the stopper surface and the socket. (Claim 6). When the working fluid of the fluid machine contains mist-like lubricating oil, the lubricating oil adheres to the inner surface of the casing. Therefore, during the reciprocation of the piston, the lubricating oil adhering to the inner surface of the case sink is guided from the stopper surface to the socket through the passage, and lubricates between the socket and the shoe.

  The piston can be made of an aluminum alloy or a magnesium alloy. In this case, it is preferable that the piston further includes an abrasion-resistant coating film on the outer surface that is in sliding contact with the inner peripheral surface of the cylinder bore and the inner surface of the casing. Such a coating film reduces wear of the piston and ensures smooth reciprocation of the piston. Further, the piston of the present invention does not require a piston ring (claim 9).

  The piston of the present invention is not limited by its shape, and may be an integrally molded product of magnesium alloy (Claim 10). In this case, the piston can be molded by semi-solid casting (Claim 11). .

  Since the piston according to claims 1 to 5 and 7 includes a plurality of reinforcing ribs connecting the piston head and the piston tail at the center of the intermediate section, the reinforcing ribs prevent the piston from being compressed or bent, and the piston Increase the rigidity. Moreover, since the outer peripheral wall of the intermediate section has a semi-cylindrical shape, it contributes to weight reduction of the piston and reduces the inertial mass of the piston. As a result, a stable and smooth reciprocating motion of the piston is ensured, and the load required to operate the fluid machine is also reduced.

The piston according to the sixth aspect can satisfactorily lubricate between the socket of the piston tail and the shoe, and the wear of the socket is reduced. Further, since the piston of claim 8 is provided with the coating film, the wear of the whole piston is also greatly reduced. Since the piston of claim 9 is not provided with a piston ring, its manufacturing cost is further reduced.
Furthermore, the pistons of claims 10 and 11 can be molded as an integrally molded product close to the final product, and the manufacturing cost of the piston can be reduced.

FIG. 1 shows a swash plate compressor as a reciprocating fluid machine. This compressor is suitable as an air conditioning system for a vehicle, that is, a refrigerant compressor for a refrigeration circuit incorporated in the air conditioning system.
The compressor includes a cylindrical housing 10, which includes a front casing 12, a cylinder block 14, and a cylinder head 16 from the left side as viewed in FIG. The front casing 12, the cylinder block 14, and the cylinder head 16 are connected to each other via a plurality of connecting bolts 18. FIG. 1 shows only one connecting bolt 18.

The front casing 12 cooperates with the cylinder block 14 to define the crank chamber 20 in an airtight manner. A drive shaft 22 is disposed in the center of the crank chamber 20, and both ends of the drive shaft 22 are rotatably supported by the front casing 12 and the cylinder block 14 via bearings.
As is apparent from FIG. 1, one end of the drive shaft 22 protrudes outside the front casing 12, and is connected to a vehicle engine (not shown) via a power transmission path. When the drive shaft 22 receives power from the engine, the drive shaft 22 is rotated in one direction.

A circular swash plate 24 is accommodated in the crank chamber 20, and the swash plate 24 is coupled to the drive shaft 22 and rotated together with the drive shaft 22. The inclination angle of the swash plate 24 with respect to the drive shaft 22 is maintained constant, or is varied by the pressure P _C in the crank chamber 20. When the inclination angle of the swash plate 24 is variable, the swash plate 24 is coupled to the drive shaft 22 via an angle variable coupler.
On the other hand, the cylinder block 14 defines a plurality of cylinder bores 26 therein, and the cylinder bores 26 are arranged at equal intervals in the circumferential direction of the cylinder block 14. The cylinder bore 26 extends parallel to the axis of the drive shaft 22 and penetrates the cylinder block 14. Further, when viewed in the radial direction of the cylinder block 14, the distance between the axis of each cylinder bore 26 and the axis of the drive shaft 22 is the same.

  A piston 28 is slidably fitted in each cylinder bore 26, and the piston 28 can reciprocate within the cylinder bore 26. Each piston 28 is operatively engaged with the outer peripheral edge of the swash plate 24 through a pair of hemispherical shoes 30. More specifically, each piston 28 has a piston tail 32, which always protrudes from the cylinder bore 26 into the crank chamber 20, and holds a pair of shoes 30 therein.

  When the swash plate 24 is rotated, each piston 28 reciprocates in the cylinder bore 26 via a pair of shoes 30. Such reciprocating motion of the piston 28 performs a process of sucking, compressing and discharging a working fluid, that is, a refrigerant. In addition, the refrigerant | coolant used for this kind of compressor contains mist-like lubricating oil, and this oil mist is used for lubrication of each mechanism part in a compressor.

More specifically, a valve plate 34 is disposed between the cylinder block 14 and the cylinder head 16. A cylinder gasket (not shown) is sandwiched between the cylinder block 14 and the bubble plate 34, and a head gasket (not shown) is sandwiched between the valve plate 34 and the cylinder head 16.
The cylinder head 16 defines a suction chamber 36 and a discharge chamber 38 in an airtight manner, and the suction chamber 36 and the discharge chamber 38 are separated from each other. In this embodiment, the suction chamber 36 is positioned in the center of the cylinder head 16, and the discharge chamber 38 has an annular shape surrounding the suction chamber 36. Incidentally, the suction chamber 36 is connected to the evaporator of the refrigeration circuit, the refrigerant of suction pressure P _S is supplied from the evaporator. On the other hand, the discharge chamber 38 is connected to a condenser of the refrigeration circuit, it supplies the refrigerant in the discharge pressure P _D to the condenser.

  The aforementioned valve plate 34 forms a compression chamber 40 in cooperation with its piston 28 in each cylinder bore 26, and this compression chamber 40 can communicate with the suction chamber 36 and the discharge chamber 38 via the suction valve and the discharge valve. is there. More specifically, the suction valve and the discharge valve include a reed valve body formed integrally with the above-described cylinder gasket and head gasket, and opens and closes the suction hole 42 and the discharge hole 44 of the valve plate 34. The suction hole 42 and the discharge hole 44 are assigned to each compression chamber 40, and the discharge valve further includes a retainer (not shown) for limiting the opening degree of the reed valve body.

Now, when the piston 28 is moved toward the crank chamber 20, the suction valve is opened, and the refrigerant in the suction chamber 36 is sucked into the compression chamber 40 through the suction hole 42. Thereafter, when the piston 28 is moved toward the valve plate 34, the refrigerant in the compression chamber 40 is pressurized, and, cutoff pressure of the pressure of the refrigerant discharge valve, i.e., if the result exceeds the discharge pressure P _D The discharge valve is opened. At this time, the high-pressure refrigerant in the compression chamber 40 is discharged into the discharge chamber 38 through the discharge hole 44.

  When the inclination angle of the swash plate 24 is controlled, the aforementioned crank chamber 20 is connected to the suction chamber 36 via an orifice passage, and connected to the discharge chamber 38 via a pressure control passage provided with a control valve. Has been. Therefore, the pressure in the crank chamber 20 is determined by the balance between the supply amount of the refrigerant supplied from the discharge chamber 38 and the discharge amount of the refrigerant escaping from the crank chamber 20 to the suction chamber 36. As a result, the inclination angle of the swash plate 24 can be controlled by the opening degree of the control valve, whereby the capacity of the compressor is varied by the inclination angle of the swash plate 24.

2 to 4 show the above-described piston 28 in detail.
As is apparent from FIG. 2, the piston 28 has a solid piston head 46 at its front end and the piston tail 32 described above at its rear end. The piston head 46 has a complete cylindrical shape and can be slidably brought into contact with the entire inner peripheral surface of the cylinder bore 26. The piston head 46 has a predetermined head length L _H in the axial direction of the piston 28, the head length L _H, through the gap between the inner peripheral surface of the cylinder bore 26 and the piston head 46, from the compression chamber 40 The refrigerant flowing into the crank chamber 20 is quantitatively limited to a predetermined range. As a result, the piston head 46 can supply a desired amount of oil mist contained in the refrigerant to the crank chamber 20 without providing a piston ring.

Further, the piston 28 includes an intermediate section 48 between the piston head 46 and the piston tail 32. The intermediate section 48 has, for example, a pair of reinforcing ribs 50 that connect the piston head 46 and the piston tail 32 to each other.
More specifically, a one-dot chain line in FIG. 3 indicates a radial plane including the axis of the piston 28 and the axis of the cylinder block 14 (that is, the axis of the drive shaft 22) when the piston 28 is fitted to the cylinder bore 26. X is shown. The pair of reinforcing ribs 50 are positioned symmetrically around the radial plane X in the vicinity of the radial plane X, and extend parallel to each other along the radial plane X. That is, the pair of reinforcing ribs 50 is disposed in the central region of the intermediate section 48.

  The thickness T of each reinforcing rib 50 and the interval S between the pair of reinforcing ribs 50 are caused by the friction between the pair of shoes 30 and the swash plate 24 described above during the reciprocating motion of the piston 28. It is determined according to the magnitude of the tangential force acting on the piston 28. That is, the pair of reinforcing ribs 50 are strength members that provide the rigidity required for the entire piston 28. Therefore, even if the above-described tangential force is applied to the piston 28, the piston 28 is not subjected to bending deformation, and even if the high pressure in the compression chamber 40 is applied to the piston 28, the piston 28 is subjected to compression deformation. Absent. As a result, the piston 28 can smoothly reciprocate within the cylinder bore 26.

Further, as shown in FIG. 2, each reinforcing rib 50 has a lower edge 52, that is, a lower edge 52 facing radially inward of the cylinder block 14 when the piston 28 is fitted in the cylinder bore 26. The lower edge 52 is inclined from the piston head 46 toward the piston tail 32 so as to be close to the axis of the piston 28. However, the portion of the lower edge 52 located on the piston head 46 side is formed as a slide guide 54, which extends parallel to the axis of the piston 28 and slides on the inner peripheral surface of the cylinder bore 26 together with the piston head 46 described above. Touch. The length L _S of the slide guide 54 is preferably slightly longer than the length L _H of the piston head 46. The above-described slide guide 54 ensures stable reciprocation of the piston 28.

  Further, the intermediate section 48 further includes a semi-cylindrical outer peripheral wall 56. The inner surface of the outer peripheral wall 56 is continuous with the upper edges of the pair of reinforcing ribs 50 and partially surrounds the reinforcing ribs 50 around the axis of the piston 28. That is, the outer peripheral wall 56 is not completely cylindrical, and has an opening region in which a part thereof is cut out, and the lower edge 52 of the reinforcing rib 50 and the slide guide 54 are exposed from the outer peripheral wall 56 through the opening region. Yes.

  More specifically, the outer peripheral wall 56 has a cross-sectional shape that is symmetric about the radial plane X described above, and this symmetry is maintained over the entire length of the outer peripheral wall 56 along the axial direction of the piston 28. . The outer peripheral wall 56 includes a large diameter portion 58 extending from the piston head 46, a small diameter portion 60 extending from the piston tail 32, and a tapered portion 62 connecting the small diameter portion 60 and the large diameter portion 58.

As shown in FIG. 4, the outer peripheral surface of the large diameter portion 58 is formed from a part of a cylindrical surface having the same diameter as the diameter D ₁ of the outer peripheral surface of the piston head 46, while the outer peripheral surface of the small diameter portion 60. Is formed from a part of a cylindrical surface having a diameter D ₂ smaller than the diameter D ₁ . The tapered portion 62 smoothly connects the large diameter portion 58 and the small diameter portion 60. Therefore, the outer peripheral wall 56 is in sliding contact with the inner peripheral surface of the cylinder bore 26 only at the large diameter portion 58.

  Further, the outer peripheral wall 56 has both side edges positioned on the sides of the pair of reinforcing ribs 50, that is, both opening edges 64. The shape of the opening edges 64 and the thickness of the outer peripheral wall 56 are determined by the piston 28. Is determined based on the CAE in consideration of the side force applied to the piston 28 during the reciprocating motion. In this case, it is desirable that the thickness of the outer peripheral wall 56 be as thin as possible. The side force is generated by the tangential force described above, and is applied to the piston 28 in the rotational direction of the swash plate 24.

Specifically, as seen in FIG. 2, each opening edge 64 has a downwardly convex arc at the large-diameter portion 58, an upwardly convex arc at the tapered portion 62, and the small-diameter portion 60. The piston 28 has a shape in which a straight line parallel to the axis of the piston 28 is sequentially connected.
Therefore, when the outer peripheral wall 56 pays attention to the circumferential length of the outer peripheral wall 56 defined between both opening edges 64, the circumferential length decreases from the piston head 46 toward the piston tail 34. It is constant at the small diameter portion 60.

Since the large-diameter portion 58 of the outer peripheral wall 56 is in sliding contact with the inner peripheral surface of the cylinder bore 26 in the same manner as the piston head 46, the amount of refrigerant flowing from the compression chamber 40 into the crank chamber 20 is adjusted in cooperation with the piston head 46. And it helps to omit the piston ring.
Further, the above-described outer peripheral wall 56 does not completely cover the pair of reinforcing ribs 50 and the thickness thereof is thin, so that the entire weight of the piston 28, that is, its inertial mass is small. Furthermore, since the outer shape of the outer peripheral wall 56, that is, the shape of the opening edge 64 is determined by CAE, the outer peripheral wall 56 also exhibits sufficient resistance to the side force described above.

Next, FIG. 5 will be added and the above-described piston tail 32 will be described in detail.
The piston tail 32 has a symmetric shape with the radial surface X as a center, and has a substantially U shape when viewed in a cross section along the radial surface X. The U-shaped piston tail 32 takes a posture of opening inward in the radial direction of the cylinder block 14 when the piston 28 is fitted into the cylinder bore 26.

Specifically, the piston tail 32 includes a pair of shoe holders 66 that are spaced apart in the axial direction of the piston 28, and a bridge 68 that connects these shoe holders 66. The reinforcing rib 50 and the outer peripheral wall 56 described above are connected to a shoe holder 66 on the front side as viewed in the axial direction of the piston 28.
As apparent from FIG. 5, the pair of shoe holders 66 have inner surfaces 70 that face each other, and shoe sockets 72 are formed on these inner surfaces 70, respectively. These shoe sockets 72 have a hemispherical concave shape and are respectively positioned on the axis of the piston 28. Each shoe socket 72 can receive the shoe 30 described above, and the pair of shoes 30 can sandwich the outer peripheral edge of the swash plate 24 while being supported by the shoe socket 72 so as to be rotatable and swingable.

  Further, as shown in FIG. 5, when the piston 28 is fitted into the cylinder bore 26, the bridge 68 has an outer surface 76 that faces the inner peripheral surface 74 of the front casing 12. A slider 78 is formed on the outer surface 76, and the slider 78 slightly protrudes from the outer surface 76 and is in sliding contact with the inner peripheral surface 74 of the front casing 12. That is, the sliding surface of the slider 78 forms a stopper surface 80 that prevents the piston 28 from rotating about the axis during the reciprocating motion of the piston 28, and the stopper surface 80 is viewed from the cross section of the piston 28 and the front casing 12. An arc shape is formed so as to match the inner peripheral surface 74.

  Further, the slider 78 is formed with, for example, three grooves, that is, oil windows 82, and these oil windows 82 are arranged symmetrically with respect to the above-described radial plane X as apparent from FIGS. 3 and 4. It extends beyond the edge of the slider 78 on the outer peripheral wall 56 side. Further, as is apparent from FIG. 5, the oil window 82 penetrates the bridge 68 when viewed in the radial direction of the piston 28, and connects between the stopper surface 80 and the inner surface of the bridge bridge 68, that is, the shoe socket 72. Form a passage.

  During the reciprocating motion of the piston 28, as described above, the slider 78 of the piston tail 32 slides with respect to the inner peripheral surface 74 of the front casing 12, and scrapes the lubricating oil adhering to the inner peripheral surface 74. As indicated by the arrows in FIG. 5, the scraped lubricating oil is guided into the piston tail 32 through the oil window 82 and supplied to the shoe socket 72. Therefore, the shoe socket 72 and the shoe 30 are well lubricated by the lubricating oil, and wear of the shoe socket 72 and the shoe 30 is reduced. The adhesion of the lubricating oil to the inner peripheral surface 74 of the front casing 12 is caused by oil mist in the refrigerant supplied into the crank chamber 20.

  The above-described piston 28 is an integrally molded product made of an aluminum alloy or a magnesium alloy. For example, when the piston 28 is made of an aluminum alloy, a forging process or a casting process can be used for forming the piston 28. On the other hand, when the piston 28 is made of a magnesium alloy, a semi-solid casting process (Thixomag (registered trademark)) can be used for forming the piston 28.

  Preferably, various sliding surfaces of the piston 28, that is, the outer peripheral surface of the piston head 46 and the outer peripheral surface of the outer peripheral wall 56 (large diameter portion 58), the slide guide 54 of the reinforcing rib 50, the outer surface of the slider 78 in the bridge 68, The shoe socket 72 is provided with a wear-resistant coating film. For example, in FIG. 5, a coating film for the outer peripheral wall 56 is indicated by reference numeral 84 in Z, which is an enlarged view of a circle Y of a one-dot chain line.

When the piston 28 is made of an aluminum alloy, the coating film 84 is made of Teflon (registered trademark). On the other hand, when the piston 28 is made of a magnesium alloy, the coating film 84 preferably has a two-layer structure of an inner layer made of an oxide ceramic base and an outer layer made of Teflon (registered trademark).
When the piston 28 described above is formed by a forging, casting process or semi-solid casting process, a set of dies or molds are used for this forming. As indicated by the one-dot chain line in FIG. 6, these die or mold separation lines PL do not include the piston 28 in the radial plane X, but include it in a plane orthogonal to the radial plane X. It is.

  More specifically, FIGS. 3 and 7 show a bottom view and a perspective view, respectively, of the piston 28 viewed from the axial side of the cylinder block 14 when it is assumed that the piston 28 is fitted to the cylinder bore 26. As apparent from FIGS. 3 and 7, the outer shape of the piston 28 does not have a recess or groove in a plane parallel to the radial surface X except for the shoe socket 72. Therefore, the piston 28 including the oil window 82 described above can be molded as an integrally molded product that is almost similar to the final product by the above-described process using a die or a mold. The shoe socket 72 is formed by machining an integrally molded product.

The present invention is not limited to the piston 28 of the above-described embodiment, and various modifications are possible.
For example, FIG. 8 shows a modified piston 86. In the description of the piston 86 of the modified example, the same reference numerals are assigned to the portions that exhibit the same functions as the piston 28 described above, and the description thereof is omitted, and the difference between the piston 86 and the piston 28. Only this will be described below.

  The piston tail 32 of the piston 86 is opposite to the pair of reinforcing ribs 50 and the outer peripheral wall 56 with respect to the diameter direction of the piston 86. In this case, the reinforcing rib 50 can have the slide guide 54 over a part or the entire length thereof. It goes without saying that the piston 86 also has the same advantages as the piston 28 described above.

It is sectional drawing which showed the swash plate type compressor. It is the side view which showed the piston of one Example. It is a bottom view of the piston of FIG. It is a top view of the piston of FIG. It is a longitudinal cross-sectional view of the piston of FIG. FIG. 4 is a cross-sectional view taken along line VI-VI in FIG. 3. It is a perspective view of the piston of FIG. It is the perspective view which showed the piston of the modification.

Explanation of symbols

12 Front casing 14 Cylinder block 24 Swash plate (swash member)
26 Cylinder bore 28, 86 Piston 30 Shoe 32 Piston tail 46 Piston head 48 Intermediate section 50 Reinforcement rib 54 Slide guide 56 Outer peripheral wall 62 Opening edge 80 Stopper surface 82 Oil window (passage)
84 Coating film

Claims (11)

A piston of a reciprocating fluid machine, wherein the fluid machine has a casing for housing a rotatable swash member, and a cylinder block, and a cylinder bore into which the piston is reciprocally fitted. A cylinder block, and a radial surface including a rotation axis of the swash member and an axis of the cylinder bore,
The piston is an integrally molded product,
A piston head, a piston tail having a socket for a shoe that engages with the swash member inside, and an intermediate section connecting between the piston head and the piston tail;
The intermediate section includes a plurality of reinforcing ribs that are arranged symmetrically around the radial surface in the vicinity of the radial surface and extend parallel to each other along the radial surface. The piston of claim 1,
The intermediate section further includes a substantially semi-cylindrical outer peripheral wall at least partially in sliding contact with the inner peripheral surface of the cylinder bore, and the outer peripheral wall partially surrounds the reinforcing rib around the axis of the piston. . The piston of claim 2,
The outer peripheral wall has a symmetrical cross-sectional shape centered on the radial surface, and has both side edges extending along the radial surface. The piston of claim 3,
The outer peripheral wall has a circumferential length defined between its opposite edges, the circumferential length being reduced from the piston head toward the piston tail. The piston of claim 3,
Each of the reinforcing ribs has a slide guide that is in sliding contact with the inner peripheral surface of the cylinder bore at least partially. The piston of claim 1,
The piston tail is
When the piston reciprocates, a stopper surface that slidably contacts the inner surface of the casing and prevents rotation about the axis of the piston;
A passage opening to the stopper surface and connecting between the stopper surface and the socket. The piston of claim 1,
The piston is made of an aluminum alloy or a magnesium alloy. The piston of claim 7,
The piston further includes a wear-resistant coating film on an outer surface that is in sliding contact with an inner peripheral surface of the cylinder bore and an inner surface of the casing. The piston of claim 2,
The piston includes a piston ringless piston head. A piston of a reciprocating fluid machine, wherein the fluid machine has a casing for housing a rotatable swash member, and a cylinder block, and a cylinder bore into which the piston is reciprocally fitted. A cylinder block, and a radial surface including a rotation axis of the swash member and an axis of the cylinder bore,
The piston is made of a magnesium alloy integrally formed product. The piston of claim 10,
The piston is formed by semi-solid casting.

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